The invention is in the field of mechanical devices for locking and guiding endless loops, such as an endless loop adapted for driving a security barrier.
Security bars may be used to cover windows and doors to secure a building. For example, U.S. Pat. No. 5,957,181 (Cohen-Ravid) discloses a security bar assembly that has a plurality of bars extending across an opening. The bars have ends that join to drive chains with bar ends that cooperate with chain links to drive the bars. A drive mechanism is disclosed that moves the drive chain such that the bars slide, and therefore cover, the opening. A variety of alternative security bar installations may be used, in which an endless loop drives the security bars. In such installations, it is desirable to provide a lock that secures the security bars in place once they have been lowered.
The invention provides a locking device adaptable for use with security bar systems. The locking device may be adapted to inhibit the movement of a drive loop which is operably connected to a security bar drive mechanism. The locking device may be adapted to engage the drive loop chain in such a way that when the security bars are closed, an attempt to open the security barrier will cause the braking device to engage the chain, locking the drive chain to prevent movement of the security bars. The lock of the invention may also be adapted for a wide variety of alternative locking or braking functions, in some embodiments serving both to lock closed security bars against an opening movement while also providing a safety mechanism that locks the bars against a closing movement when an object, such as a person""s arm, interferes with the closing movement of the bars (to help prevent injuries caused by movement of the bars).
In one aspect, the invention provides an endless loop lock including a drive wheel adapted to be driven or not driven. The drive wheel may have a resistance to rotation when an external force attempts to move the drive wheel at a speed that is different from the drive speed. For example, such resistance may be provided by a drive wheel that is driven by an electric motor, wherein the motor may offer a resistance to any rotational movement when it is not energized, or a resistance to rotation at any speed other than the speed at which the motor is being electrically driven. The drive wheel accordingly acts as a tensioning mechanism, and provides a means for exerting tension on the endless loop, by providing a mechanism that engages the endless loop in a manner capable of resisting movement of the endless loop. In alternative embodiments, other mechanisms may be provided as means for exerting tension on the endless loop, such as a sprocket or guide that does not serve as a drive wheel because it is not driven.
An endless loop, such as a chain, may be provided, engaging the drive wheel or alternative means for exerting tension on the endless loop. In some embodiments, the endless loop may be adapted to be driven by the drive wheel to move a device, such as a security bar, connected to the endless loop. A guide may be provided, biased against the endless loop at a position spaced apart from the drive wheel.
A lock may be provided, for engaging the endless loop to inhibit movement of the endless loop, the guide being positioned to bias the endless loop out of engagement with the lock when the endless loop is not under a locking tension, such as when the endless loop is driven by the drive wheel. The lock may for example be actuated by a force applied to a device connected to the endless loop when the drive wheel is not driven, or when the device is urged to move more quickly or more slowly than the speed conferred by the drive wheel, so that a locking tension is applied to the endless loop. The lock may accordingly be actuated when the force applied to the device urges the device connected to the endless loop to move against the resistance to rotation afforded by the drive wheel. In alternative embodiments, the resistance to movement may be provided by a clamp that engages the endless loop, a sprocket engaging the endless loop or alternative means for exerting tension on the endless loop. The force applied to the device exerts a locking tension on the endless loop, the locking tension being between the device and the drive wheel (or clamp or alternative means for exerting tension on the endless loop), so that the locking tension is exerted across the guide member The endless loop thereby engages the lock when the locking tension on the endless loop is sufficient to displace the guide (which may be detected by a detector to provide an indication that the lock has been actuated). The engagement of the endless loop by the lock may prevent movement of the endless loop, as in the case of splines on a fixed gear that engage a chain. Alternatively, the engagement of the endless loop by the lock may serve merely to inhibit the movement of the endless loop, providing a braking effect.
In some embodiments, the lock includes four elements: an endless loop, a mechanism for tensioning the loop, a device attached to the loop which may be used to exert force on the loop against the tension provided by the tensioning mechanism and a lock or locking member which is engaged when sufficient tension is applied to the loop. The loop engages the tensioning mechanism, such as a drive wheel, at a first portion of the loop, and engages the lock at a second portion of the loop. The lock is engaged when force is exerted on the loop by the device towards the tensioning mechanism, so that the second portion of the loop is subject to sufficient tension.